common/Input: Avoid not-recommended way of using react-intl API.

Following from discussion on GitHub [1].

We would have a bug if multiple chunks were passed to the render
callback prop [2], since we're just using the first one. It looks
like multiple chunks won't be passed, since we haven't explicitly
made that happen.

Glad to have this API misuse exposed by the API change in
`react-intl` v5, which we took in a recent commit:
"`FormattedMessage` render prop is no longer variadic".

But we don't need to use this render prop pattern at all. From the
docs [3]:

"""
If you need to customize rendering, you can either [...] or pass a
function as the child.
"""

We just need plain old strings, without customization. So, just do
the more straightforward thing we do in a bunch of places: use
`formatMessage` as it's wrapped by `_`. Plumb through `_` using
`withGetText` as recommended by the JSDoc for `GetText`:

"""
Alternatively, for when `context` is already in use: use
`withGetText` and then say `const { _ } = this.props`.
"""

[1] #4222 (comment)
[2] The render callback prop's name is `children`. The "Function as
    Child Component" pattern is sometimes opposed because `children`
    is rarely an appropriate, expressive name; see, e.g.,
    https://americanexpress.io/faccs-are-an-antipattern/. Here, it
    also doesn't seem to be well-typed in the libdef. I'm unsure if
    the "FaCC" pattern makes it especially hard to get well-typed,
    but it seems plausible.
[3] #4222 (comment)

src/common/Input.js

@@ -1,17 +1,19 @@
 /* @flow strict-local */
 import React, { PureComponent } from 'react';
 import { TextInput, Platform } from 'react-native';
-import { FormattedMessage } from 'react-intl';
 
-import type { LocalizableText } from '../types';
+import type { LocalizableText, GetText } from '../types';
 import type { ThemeData } from '../styles';
 import { ThemeContext, HALF_COLOR, BORDER_COLOR } from '../styles';
+import { withGetText } from '../boot/TranslationProvider';
 
 export type Props = $ReadOnly<{|
   ...$PropertyType<TextInput, 'props'>,
   placeholder: LocalizableText,
   onChangeText?: (text: string) => void,
   textInputRef?: (component: ?TextInput) => void,
+
+  _: GetText,
 |}>;
 
 type State = {|
@@ -32,7 +34,7 @@ type State = {|
  * @prop ...all other TextInput props - Passed through verbatim to TextInput.
  *   See upstream: https://reactnative.dev/docs/textinput
  */
-export default class Input extends PureComponent<Props, State> {
+class Input extends PureComponent<Props, State> {
   static contextType = ThemeContext;
   context: ThemeData;
 
@@ -77,37 +79,31 @@ export default class Input extends PureComponent<Props, State> {
   };
 
   render() {
-    const { style, placeholder, textInputRef, ...restProps } = this.props;
+    const { style, placeholder, textInputRef, _, ...restProps } = this.props;
     const { isFocused } = this.state;
     const fullPlaceholder =
       typeof placeholder === 'object' /* force linebreak */
         ? placeholder
         : { text: placeholder, values: undefined };
 
     return (
-      <FormattedMessage
-        id={fullPlaceholder.text}
-        defaultMessage={fullPlaceholder.text}
-        values={fullPlaceholder.values}
-      >
-        {(chunks: string[]) => (
-          <TextInput
-            style={[this.styles.input, { color: this.context.color }, style]}
-            placeholder={chunks[0]}
-            placeholderTextColor={HALF_COLOR}
-            underlineColorAndroid={isFocused ? BORDER_COLOR : HALF_COLOR}
-            onFocus={this.handleFocus}
-            onBlur={this.handleBlur}
-            ref={(component: ?TextInput) => {
-              this.textInput = component;
-              if (textInputRef) {
-                textInputRef(component);
-              }
-            }}
-            {...restProps}
-          />
-        )}
-      </FormattedMessage>
+      <TextInput
+        style={[this.styles.input, { color: this.context.color }, style]}
+        placeholder={_(fullPlaceholder.text, fullPlaceholder.values)}
+        placeholderTextColor={HALF_COLOR}
+        underlineColorAndroid={isFocused ? BORDER_COLOR : HALF_COLOR}
+        onFocus={this.handleFocus}
+        onBlur={this.handleBlur}
+        ref={(component: ?TextInput) => {
+          this.textInput = component;
+          if (textInputRef) {
+            textInputRef(component);
+          }
+        }}
+        {...restProps}
+      />
     );
   }
 }
+
+export default withGetText(Input);

src/common/InputWithClearButton.js

@@ -14,7 +14,7 @@ const componentStyles = createStyleSheet({
   },
 });
 
-type Props = $ReadOnly<$Diff<InputProps, { textInputRef: mixed, value: mixed }>>;
+type Props = $ReadOnly<$Diff<InputProps, { textInputRef: mixed, value: mixed, _: mixed }>>;
 
 type State = {|
   canBeCleared: boolean,

src/common/PasswordInput.js

@@ -27,7 +27,7 @@ const styles = createStyleSheet({
 type Props = $ReadOnly<$Diff<InputProps,
   // "mixed" here is a way of spelling "no matter *what* type
   // `InputProps` allows for these, don't allow them here."
-  { secureTextEntry: mixed, autoCorrect: mixed, autoCapitalize: mixed }>>;
+  { secureTextEntry: mixed, autoCorrect: mixed, autoCapitalize: mixed, _: mixed }>>;
 
 type State = {|
   isHidden: boolean,