Currently the expressions used in a template string are automatically named
`PH_1`, `PH_2`, etc. Whereas interpolations used in i18n templates generate
placeholders automatically named `INTERPOLATION`, `INTERPOLATION_1`, etc.
This commit aligns the behaviors by starting the generated placeholder
names for expressions at `PH`, then `PH_1`, etc.
It also documents this behavior in the documentation of `$localize` as
it was not mentioned before.
PR Close#32493
f1b1de9a3d