[feature] Allow regexes when patching files (tools.replace_regex_in_file)

[madebr]

Often, when packaging external software, patching is required.
Right now the main tools we have are:

• tools.replace_in_file (tools.replace_path_in_file, tools.replace_prefix_in_pc_file)
• tools.save_append
• tools.patch

Having the ability to use regex'es to patch sources would be nice.

Example usage:
conan-io/conan-center-index#1607.

This contans a for loop with 2 replaces:

for e in ["MDd", "MTd", "MD", "MT"]:
    tools.replace_in_file(filename, "/%s " % e, "/%s " % self.settings.compiler.runtime, strict=False)
    tools.replace_in_file(filename, "/%s\"" % e, "/%s\"" % self.settings.compiler.runtime, strict=False)

A regex can replace this with:

tools.replace_regex_in_file(os.path.join(filename, "/M[TD]d?([\" ])", "/{}\\1".format(self.settings.compiler.runtime))

Notice also how the strict=False can be removed which gives greater confidence that a patch is working.

example implementation (not tested):

import re


def replace_regex_in_file(file_path, pattern, repl, flags=None, strict=True, output=None, encoding=None):
    output = default_output(output, 'replace_regex_in_file')

    encoding_in = encoding or "auto"
    encoding_out = encoding or "utf-8"
    content = load(file_path, encoding=encoding_in)

    content, nb = re.subn(pattern, repl, content, flags=flags)
    if nb == 0:
        _manage_text_not_found(pattern, file_path, strict, 'replace_regex_in_file', output=output)

    content = content.encode(encoding_out)
    save(file_path, content, only_if_modified=False, encoding=encoding_out)

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